A network is typically represented as a set of nodes and links between the nodes. In networking for data communication, a protocol may be chosen for the communication of a traffic flow from a source node to a destination node based on such factors as a Quality of Service (QoS) requirement of the traffic flow and information known about the links in the path from the source to the destination. A network may be defined in part by the manner in which it determines a route from source to destination (routing) and the manner in which multiple traffic flows share individual links along the route (multiplexing).
Increasing requirements for capacity in data networks is, to a large extent, being met by communication links over which communication is accomplished by modulating an optical signal, such as a beam of light, to represent binary coded data. Such networks are called optical networks. One of the strengths of optical networks is found in long distance communication. As such, two geographically separated service networks that use electrical links may be connected through the use of an optical network. An optical network used for this purpose may be called a transport network and will often use a communication protocol different than that in use in the service networks.
To make efficient use of an optical medium (such as glass fiber), many unique data signals may be transmitted over the same fiber so long as each data signal modulates an optical signal with a wavelength different from the other optical signals on the same fiber. When the wavelengths of the different optical signals are only marginally different from one another, the transmission scheme may be called Dense Wavelength Division Multiplexing (DWDM). In a network using DWDM, two elements connected by a single fiber may communicate using a number of optical signals, each with a distinct wavelength. Each optical signal (at a single wavelength) may be called a “Lambda” and be described in terms normally associated with an entire link between elements, such as bandwidth and delay.
Time division multiplexing (TDM) is another way of transmitting several data signals over a single link. In TDM schemes, streams of digital data are broken up into segments, for instance “octets” which are sequences of eight bits, which may also be called bytes. The North American standard for digital networks that employ optical fiber is called Synchronous Optical Network (SONET). The European and ITU-T (Telecommunication Standardization Sector of the International Telecommunications Union) standard is called Synchronous Digital Hierarchy (SDH). Both use octet multiplexing to create a higher-speed stream from several lower-speed tributary signals. In octet multiplexing, successive time slots on a carrier signal are allocated to octets from different tributaries. In a SONET based transmission system, the multiplexed output of a node may be a “Synchronous Transport Signal Level 1 (STS-1)” frame with a basic bit rate of 51.84 Mbps. When such a frame is transmitted on an Optical Carrier, it is said to be an Optical Carrier Level 1 signal, or OC-1. Along a path from a source to a destination, STS-1 frames may be multiplexed together into a higher order frame, such as an STS-3 frame carried on an OC-3 signal. An OC-3 signal is said to have three STS-1 time slots.
The multiplexing methods above may be used alone or in combination. When used in combination, a single fiber between two nodes may, for example, carry a first Lambda which is an OC-3 signal carrying three STS-1 time slots and a second Lambda which is an OC-48 signal carrying four OC-12 signals, each carrying three OC-3 signals which each carry three STS-1 time slots, for a total on the second Lambda of 48 STS-1 time slots.
Various routing schemes have been developed for determining an optimum path from source to destination. In particular, Open Shortest Path First (OSPF) is a routing scheme which involves including an indication of the address of a source and destination of an OSPF protocol data unit (PDU) within the PDU. Each node, in a given network using OSPF, maintains an identical database describing the topology of the given network, i.e., which nodes have links to which other nodes and the state and qualities of those links. From information in the topology database, a routing table may be calculated. A routing table stores a “shortest” path from each node to each other node. Upon receiving an OSPF PDU, a node may extract the address of the destination node of the PDU. The node then consults the routing table to determine the next node in the shortest path to the destination node, determines the identity of the link to the next node and transmits the OSPF PDU to the determined next node over the identified link.
Multi-Protocol Label Switching (MPLS) is a technology for speeding up network traffic flow and increasing the ease with which network traffic flow is managed. As in OSPF, each node maintains an identical database describing the topology of the given network. Prior to sending an MPLS PDU, the source node uses the topology database to predetermine a path to the destination node. The nodes along the predetermined path are then informed of the next node in the path through messages sent by the source node to each node in the predetermined path, where each node uses information contained in the received message to associate a “label” with a mapping of an ingress connection from the previous node to an egress connection to the next node. By including, at the source node, the label in each MPLS PDU sent to the destination node, the time that would be otherwise needed for a node to determine the next node to which to forward a PDU is saved. The path arranged in this way is called a Label Switched Path (LSP). MPLS is called multiprotocol because it works with the Internet Protocol (IP), Asynchronous Transport Mode (ATM) and frame relay network protocols. An overview of Multi Protocol Label Switching (MPLS) is provided in R. Callon, et al, “A Framework for Multiprotocol Label Switching”, Work in Progress, November 1997, and a proposed architecture is provided in E. Rosen, et al, “Multiprotocol Label Switching Architecture”, Work in Progress, July 1998, both of which are hereby incorporated herein by reference.
A fundamental concept of MPLS is that two Label Switching Routers (LSRs) must agree on the meaning of the labels used to forward traffic between and through each other. This common understanding is achieved by using a set of procedures, called a label distribution protocol, by which one LSR informs another of label bindings it has made. The MPLS architecture does not assume a specific label distribution protocol.
Label distribution protocols that have been proposed include LDP (Label Distribution Protocol) and a constraint-based extension to LDP called CR-LDP. Further label distribution protocols include RSVP (Resource ReSerVation Protocol) and an extension to RSVP called RSVP-TE. LDP is described in detail in Loa Andersson, et al., LDP Specification, Internet Engineering Task Force (IETF), Internet Draft, draft-ietf-mpls-ldp-06.txt, October 1999 which is hereby incorporated herein by reference and referred to hereafter as “the LDP specification”. Constraint-Based Routing (CR) offers the opportunity to extend the information used to set up paths beyond what is available for the routing protocol. For instance, an LSP can be set up based on explicit route constraints, QoS constraints, etc. CR-LDP, as defined in Bilel Jamoussi, “Constraint-Based LSP Setup using LDP,” draft-ietf-mpls-cr-ldp-03.txt, Work in progress, September 1999, and hereby incorporated herein by reference, specifies mechanisms and parameters for support of CR-LSPs using LDP. RSVP-TE is described in detail in Awduche, et al, “RSVP-TE: Extensions to RSVP for LSR Tunnels,” draft-ietf-mpls-rsvp-lsp-tunnel-05.txt, Work in progress, September 1999, which is also hereby incorporated herein by reference and specifies extensions to RSVP for establishing LSPs in MPLS networks.
A sending LSR using LDP associates a Forwarding Equivalence Class (FEC) with each LSP it creates. The FEC associated with a particular LSP specifies which PDUs are associated with the particular LSP. LSPs are extended through a network as each LSR “splices” incoming labels for a given FEC to the outgoing label assigned to the next hop for the given FEC. In contrast, RSVP provides setup of resource reservations for multicast or unicast data flows initiated at a receiving LSR.
Routing schemes, as mentioned above, require information about links in the network through which data is to be routed. Traditionally, the information available regarding links in a network has related only to the link between a given pair of nodes. In an optical network, network topology information for this link may be said only to be available at the fiber granularity level. However, with the advent of DWDM, routing schemes exist (many based on MPLS) which employ network topology information available at the Lambda granularity level.
When designing a protocol for use in an optical label switching network, two issues arise. One issue relates to the effective representation of optical network resources (such as optical bandwidth) in a label, so as to provide a description of network topology information at various levels of granularity. Further, as an optical network may act as a transport network, a second issue relates to the representation of information regarding the interface between a service network and a transport network at the ingress to the transport network, so that the interface information may be confirmed at the egress of the transport network.